Abstract

We have developed a simple, high-speed, nearly vibration-free, mechanically scanned, optical delay line suitable for femtosecond time-resolved signal-averaging measurements. We demonstrate a 2-ps time window autocorrelator with a display updated at 400 Hz. The delay line uses a dithering planar mirror as a time-varying linear phase ramp in the spectral plane of a modified grating–lens femtosecond pulse shaper. The time delay is linearly proportional to the angular deviation of the mirror. The high speed and low vibration are a result of the extremely small angular changes required to generate a large time delay.

Figures (2)

The RSOD consists of a grating placed in the focal plane of an achromat of focal length f and a planar mirror in the opposite focal plane. The mirror is free to dither about the pivot point under the influence of a PZT actuator and return springs (not shown). The optical carrier frequency ω0 is assumed to propagate along the symmetry (y) axis. One input ray representing the optical frequency ω(solid line) is shown and labeled by the spectral frequency Ω = ω − ω0. It is diffracted at an angle Δθ from the y axis. The diffraction causes the ray to be offset a distance Δx at the mirror plane. The returning ray (dashed line) is slightly offset owing to the mirror tilt described by the slope s. This slope causes the path length of the ray Ω to differ from the path length of the carrier frequency ray by an increment Δy = sΔx.

Triggered oscilloscope traces of autocorrelations of a 100-fs optical pulse and the driving voltage waveforms (complete cycle) obtained from a modified background-free autocorrelator incorporating the RSOD. The PZT is driven by a (a) 100-Hz triangular and a (b) 400-Hz sinusoidal waveform. The PZT contracts on the first half of the trace.